In the operation of large vapor generators which are used in connection with the production of electrical power, various types of oil and gas burners are utilized. The fuel is usually well mixed with air in and near the burner in order to obtain proper combustion. This generally results in the production of relatively high levels of oxides of nitrogen which are generally referred to as nitric oxides, which cause a severe air pollution problem. Thus, in accordance with the present invention, it is possible to substantially reduce the levels of nitric oxides which heretofore have been produced in prior burner systems. Accordingly, it is possible to meet governmental air pollution requirements for the emission of nitric oxides in vapor generators, by the provision of a primary burner which operates with a fuel-rich mixture with the balance of the air required for combustion being supplied at a secondary location at a suitable distance from the primary burner. It is also possible to utilize the present invention without burning a fuel-rich mixture, and the burner unit of the present invention can be operated with an air-rich mixture for conventional light-off and firing conditions. Thus, the primary objective of the present invention is to provide a simplified system for reducing the levels of nitric oxides produced in large vapor generators. This is achieved by providing a burner cylinder within which it is possible to create recirculation patterns for establishing a near stoichiometric flame stabilization zone in which recirculation gases and atomized oil are injected for combustion, such that the balance of the inected fuel is vaporized and mixed with the incoming air for discharge into the furnace region of the vapor generator where the mixture burns in a non-adiabatic fashion. In this manner, low levels of nitric oxide are achieved together with high levels of combustion efficiency. This results in a condition of superior flame stability in which it is possible to maintain continuous ignition. It should be understood that while the burner unit of the instant invention does have great application for use in vapor generators, applicant's burner also can be used in any variety of furnace uses, such as for example, kilns, drying applications, chemical processes, and fired heaters.